This invention relates to simultaneous electrodeposition of Co-Cr and Co-Cr-Mo alloys onto a base surface during a single electroplating operation. The process accomplishes concurrent deposition of Co and Cr, or Co, Cr and Mo metal atoms, thus creating a homogenous "alloy" surface coating. This electrodeposition process can be applied to fix calcium phosphate ceramics to substrates.
In U.S. application Ser. No. 565,936, filed Aug. 13, 1990, by T. E. Taylor, et al, there is disclosed a process for codeposition of bio-compatible ceramic materials, i.e. calcium phospates and in particular hydroxyapatite (HA), from the same solution during electrodeposition of a metal, such as cobalt, on a suitable substrate or base surface. The objective was to mechanically bond non-metallic bio-compatible ceramic particles to a substrate material by surrounding the particles with electrodeposited metal atoms, thus creating a superiorly bonded composite surface coating containing both metallic and non-metallic materials.
Heretofore, most chromium plating has been, and continues to be, performed using the hexavalent form of chromium as the dichromate ion. Such a process uses an extremely acidic solution which may be detrimental to other materials (i.e., calcium phosphates such as HA) that would be exposed in the plating bath during fixation by the depositing alloy.
Corrosion-resistant chromium-containing alloys, such as cobalt-chromium alloys and particularly cobalt-chromium-molybdenum alloy, a high strength corrosion resistant alloy, have numerous applications. Potential uses for such alloy-plated surfaces are metal structures which are exposed to corrosive environments such as chemical processing equipment. Still another application is prosthetic devices for which this type of alloy is FDA approved--where corrosion resistance and bio-compatibility of a device implanted in living-tissue is of prime importance.
However, as previously noted, not only has the deposition of chromium from electrolytic plating baths required highly acidic solutions, but when attempting to electrolytically plate an alloy containing cobalt and chromium by codeposition thereof, the kinetic rate for cobalt deposition is extremely fast relative to that for chromium, so the resulting electroplated alloy contains only a very small percentage of chromium, and the most desirable alloys of cobalt and chromium, e.g. containing from about 12 to about 33% by weight of chromium, cannot be successfully electrodeposited. Thus, for example, alloys such as Casteloy and Vitallium, containing cobalt, chromium and molybdenum, e.g. used for medical implants, are normally produced by melting, mixing and solidifying these elements in the desired proportions.
It is an object of the present invention to provide a process for electrolytically codepositing at least a two-component system composed of cobalt and chromium.
Another object is the provision of a process of the above type employing a mildly acidic electrolyte solution.
Still another object is to provide a process as noted above using an electrolytic solution under conditions to codeposit at least a two-component system composed of cobalt and a predetermined substantial proportion of chromium.
Yet another object is the provision of a process for electrolytically codepositing a three component system consisting of cobalt, chromium and molybdenum.
Another object is the provision of a process of the above type employing trivalent chromium baths.
A still further object is to provide a process for electrolytically codepositing a three component system consisting of cobalt, chromium and molybdenum, to fix ceramic materials such as a calcium phosphate, e.g. HA, to a substrate surface.